This invention relates to the removal of marine fouling from structures exposed to a marine environment, and in particular ships"" hulls.
The fouling of underwater structures by marine organisms is a well-known problem. Both static structures such as oil platforms, and mobile structures such as ships are affected. In the case of ships, the accumulation of marine growth can drastically reduce a vessel""s speed and increase fuel consumption. As a result, ships must be regularly serviced to remove this growth. The servicing of ships, however, is very expensive, not only in terms of direct costs but also in lost revenues while the ship is idle. Consequently, increasing the speed with which this work is performed is critical.
Of the various types of organisms that comprise marine fouling, one of the post troublesome is the barnacle. This organism, which outwardly resembles a mollusk, is actually a crustacean, of the class cirripedia. In its larval stage, the barnacle attaches itself headfirst to a substrate such as a ship""s hull, and thereafter constructs a shell composed of six calciferous plates. The animal attaches these plates to the substrate with one of the most powerful adhesives known in nature, which makes removal of the shell extremely difficult. Barnacles are particularly troublesome because these shells remain attached even after the animal is dead.
Various methods have been developed for killing marine growth, however these methods do not address the problem of removing the organisms after they have been killed. U.S. Pat. Nos. 5,327,848; 5,2401,674; and 5,593,636 disclose the use of heat for killing zebra mussels. These patents disclose that the use of temperatures in the order of 35-45 degrees Centigrade is sufficient to achieve adequate mortality. U.S. Pat. No. 5,804,065 discloses the use of a low-level electric field to kill marine growth. This patent teaches that subjecting zebra mussels to a field having a power density between about 3,500 to 50,000 microwatts/cubic centimeter for a time interval of about 24 to 72 hours is sufficient to achieve adequate mortality. These patents do not disclose, however, any effect on the adhesive properties of barnacle shells to a substrate, nor provide a means for the removal of such shells. In particular, the time intervals disclosed by U.S. Pat. No. 5,804,065 demonstrates that the technique disclosed therein is aimed at stopping the reproduction and propagation of the organisms, and is consequently unsuitable for the efficient cleaning of hulls or other substrates.
It is therefore an object of the current invention to provide an apparatus and method for removing marine fouling from a substrate, in particular marine organisms such as barnacles, which attach to the substrate with the help of a natural adhesive. It is a further object of the invention to provide an apparatus and method that improves the speed and efficiency with which marine fouling can be removed. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
The present invention is directed to an improved method and apparatus that takes a novel approach for removing marine fouling from underwater structures such as ships"" hulls. The method is characterized by the steps of first subjecting marine organisms such as barnacles to an electrical field of sufficient intensity to degrade the adhesive properties of the organisms to a substrate, and thereafter physically removing said organisms with the help of rotating brushes or similar abrasive removal means. The apparatus is characterized in that it includes a remotely operated submarine or other suitable transport means, such as a vehicle with a magnetized caterpillar track, having a forwardly mounted electrode for imparting an electric field to the organism=together with abrasive removal means mounted behind the electrode for removal of the organisms.